Gas Exchange Mechanisms in Insects

May 22, 2025

Lecture Notes: Gas Exchange in Terrestrial Insects

Overview

  • Focus on gas exchange in terrestrial insects
  • Anatomy, adaptations, and water loss prevention

Anatomy of Terrestrial Insects

  • Exoskeleton
    • Made of chitin: hard, fibrous material for protection
    • Contains a lipid layer to prevent water loss
  • Ventilation and Gas Exchange
    • No lungs
    • Tracheal system instead

Adaptations to Limit Water Loss

  • Essential for survival on land (terrestrial environment)
  • Key Adaptations:
    1. Small Surface Area to Volume Ratio
      • Limited water evaporation surface
    2. Lipid Layer
      • Makes the exoskeleton waterproof
    3. Spiracles
      • Tiny holes on the abdomen for gas exchange
      • Can open and close to control water loss

Tracheal System

  • Components: Spiracles, Tracheae, Tracheoles
  • Spiracles
    • Valve-like openings along the abdomen
    • Control water loss and gas entry/exit
  • Tracheae
    • Network of internal tubes
    • Rings to strengthen and prevent collapse
  • Tracheoles
    • Smaller tubules branching from tracheae
    • Deliver oxygen to respiring cells

Gas Movement in the Tracheal System

  1. Simple Diffusion
    • Oxygen used up, carbon dioxide produced by respiring cells
    • Concentration gradient allows diffusion
  2. Mass Transport
    • Muscle contractions in the abdomen move gases
    • Increases volume of gases exchanged
  3. Fluid Pressure Changes
    • Occurs during flight
    • Switch to anaerobic respiration producing lactate
    • Lowers water potential, causing water movement
    • Decreases pressure and volume in tracheoles, drawing in air

Summary

  • Large Surface Area: Numerous fine tracheoles and spiracles
  • Short Diffusion Pathway: Thin tracheole walls, short distance between spiracles and tracheal system
  • Maintaining Concentration Gradient: Respiring cells use oxygen, produce carbon dioxide
  • Importance of maintaining a steep diffusion gradient for efficient gas exchange